Recording - April 2011 - 44

Measuring Your Latency Try this simple test setup (Figure 4A) if you want to learn how much latency you actually have.

Alternate solutions An analog mixer offers true zero-latency monitoring, with the bonus of flexible signal routing and control. Today’s inexpensive mixers provide excellent sound quality as long as you’re careful to avoid clipping. You might be short on table space or prefer to spend your money on another microphone or plug-in, but I still heartily recommend a mixer-based system. It resolves many issues beyond monitoring latency. Some audio interfaces include a built-in monitor mixer independent of the computer. Stereo interfaces with this feature usually have an analog mixer, offering real zero-latency, while multi-channel interfaces typically use a DSP-based digital mixer. Since the signal goes through the A/D and D/A converters on its way in and out of the DSP, converter latency plus the short DSP latency (typically 2–3 ms total) will be present, but it’s consistent and requires no tweaking. Why DSP? It’s cheaper than building a multi-channel analog mixer. Many mixers are now available with a built-in FireWire or USB interface, combining mic preamps, direct input monitoring, and computer I/O into a single unit. This is a great approach if you need a mixer for your band’s PA and like to record your shows.

FIG. 4A
Connect the output of Channel 1 of your sound card or interface to the input of Channel 2. The input can be from a microphone (clap your hands or hit a drum), a metronome, or a drum machine. You want a sound that has a sharp attack. The headphones are optional if you want to be sure that things are working. Open up a DAW program and set it up to record on two tracks, or a single stereo track. Turn Input Monitoring ON. If you’re recording two mono tracks, pan Channel 1 fully left and Channel 2 fully right. Start up your drum machine or make some noise and adjust levels so that you can see an input on both tracks. If your DAW has automatic latency compensation, turn it off. You may need to find the latency compensation setting in a menu and manually set it to zero. Record a couple of seconds. Stop, and zoom in very close. You’ll see that Channel 2 is recorded a bit later than Channel 1 (see Figure 4B).

TOO LITTLE BUFFERING, AND YOUR AUDIO WILL STUTTER. TOO MUCH, AND LATENCY WILL HAUNT YOU.

When recording vocals, try the time-honored technique of removing one earphone to hear your own voice acoustically. Many people sing better this way even when there’s no latency problem. Remember to mute the output of the vocal track in the DAW monitor mix so it won’t distract you. When recording a virtual instrument track, listen to a built-in keyboard patch through a small powered speaker or use a small guitar amplifier rather than the virtual instrument you’ll be using in the final mix. Late enough? It’s difficult to quit fooling with a computer. There are always improvements to be made. Hopefully some of these suggestions will help you to get more comfortable with monitoring while tracking. A comfortable musician is a better musician. Mike Rivers (rivers@recordingmag.com) is a recording engineer and audio boffin in the Washington, DC area. Resources Tips for optimizing a Windows PC: Digital Producer: www.digitalproducer.com/2002/11_nov/features/11_04 /optimize_pcaudio.htm ASIO4ALL ASIO Driver for WDM sound cards (free download): www.asio4all.com DPC Latency Checker (free download): www.thesycon.de/deu/latency_check.shtml How to disable Auto-Run in Windows XP (Microsoft Knowledge Base): support.microsoft.com/kb/953252 An excellent article on using a mixer with a DAW by Ethan Winer: www.ethanwiner.com/mixer2daw.html

FIG. 4B

The selected portion of this display shows the time offset between the negative-going leading edge of this metronome click. The arrow in the lower right corner is pointing to the selection length in samples. The buffer setting is 64 samples, but the actual latency is 105 samples or 2.5 ms (44.1 kHz sample rate).
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http://www.digitalproducer.com/2002/11_nov/features/11_04/optimize_pcaudio.htm http://www.digitalproducer.com/2002/11_nov/features/11_04/optimize_pcaudio.htm http://www.asio4all.com http://www.thesycon.de/deu/latency_check.shtml http://support.microsoft.com/kb/953252 http://www.ethanwiner.com/mixer2daw.html

Recording - April 2011

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